This invention relates to improvements in fibrous web formation wherein an aqueous fibrous suspension is dewatered on a forming surface to provide a web which may be further processed into a single ply web or may be joined while wet with additional wet webs to form a multilayer web. More particularly, the invention relates to improvements in web forming apparatus of the type known in the art as twin wire formers wherein a slurry of fibrous stock is delivered from a head-box slice opening to a forming throat between a pair of endless travelling forming wires between which the web is dewatered by being squeezed between the forming wires which are often more generically referred to as forming belts.
Within recent times the art of papermaking has undergone a number of significant advances in web formation using two opposed forming belt runs for web formation therebetween as contrasted to the more conventional Fourdrinier type papermaking machine employing only a single forming wire. The twin belt forming machines have met with substantial commercial success since they offer advantages of requiring less space and improved dewatering at high speeds. As the speed of the papermaking machines has increased, it has become increasingly difficult to handle and control the high speed travelling fibrous web and to determine with a certainty the continued position of the web and to insure that it will follow the desired forming or carrying belt. In the manufacture of lightweight paper webs, such as tissue, it is increasingly difficult to insure that the paper not be damaged at the point of wire separation due to splitting of the web at that point and the problem is one of insuring that most of the fiber will follow one or the other of the forming or carrying wires or belts. These problems are particularly present in apparatus adapted for multi-ply web formation.
Efforts to solve the problems have resulted in teachings of the art that various and sundry suction mechanisms such as suction rolls and suction boxes must be positioned at proper locations to insure that the web will remain stapled or adhered to the desired wire when necessary, and will be separated from one wire or belt and properly transferred to another wire or belt as necessary. The requirement for providing suction boxes or suction rolls requires additional cost and space for pumps and other ancillary parts that wear and require maintenance.
An example of prior art teaching is found in U.S. Pat. No. 3,543,834, Stuebe, which does provide a fairly compact multi-layer web former, but still requires suction roll equipment.
In U.S. Pat. No. 3,876,498, Justus, suction roll equipment is dispensed with, but adaptation for multi-ply web forming is not taught, the formed web being picked off from the inner wire or belt after the web is so thoroughly dewatered that it is no longer stapled to the inner wire but is easily removable. Therefore after the dewatered web is picked off of the inner belt, it is no longer possible to integrate it with one or more other newly formed webs to provide a multi-ply web.